Effect of Copper in a Distillation Apparatus on Dimethyl Trisulfide Levels in Imo-Shochu

Sweet potato shochu (imo-shochu) is a popular traditional Japanese distilled spirit. Copper stills are known to affect the flavor of imo-shochu. However, its effects on imo-shochu quality, particularly dimethyl trisulfide (DMTS) concentration, remain unclear. Copper plates were installed at four different sections of a glass distillation apparatus, and the effects of varying their positions on DMTS concentrations in imo-shochu were evaluated. Additionally, a DMTS solution was distilled under the same procedure to investigate the reduction and potential adsorption of DMTS by copper. As a result, installing copper plates in all four sections reduced the DMTS concentration. Altering the plate positions revealed that copper installed in the condenser was particularly effective to reduce the DMTS concentration. The DMTS concentration in unheated moromi were below the limit of quantification and DMTS was generated upon heating. It is suggested that DMTS in imo-shochu is formed during the distillation process. Although distillation of the DMTS solution confirmed that DMTS adsorbs onto the copper plate installed in the condenser, the adsorption ratio was relatively low. These results suggest that copper reduces DMTS through mechanisms beyond physical adsorption, and that its effectiveness may depend on the properties of the liquid being distilled and the extent of contact between DMTS and the copper surface.